Magnetic tape is a widely used media for the storage of data. To write and read data to and from the tape, it is moved longitudinally past one or more magnetic transducers usually containing several read/write poles. To achieve higher data capacities, the industry is moving to thinner media that allows for longer tapes to reside in existing standardized cartridges, and the width of the data tracks have decreased to allow for more data tracks on a tape.
The thinner tapes require gentle mechanical support due to their flexibility. When the tape guides exert too much force against the tape edges, the tape can buckle or the edges will be subject to excessive wear. The tension across the tape must also be kept uniform. Otherwise, the tape will not exert enough pressure against the transducer resulting in poor read/write characteristics. In some applications, the tape path requires the guides to be in contact with the magnetic side of the tape. Where this happens, the guide-to-tape wear should be kept low to reduce the potential for damage to the magnetic layer and the data stored within.
The narrower data track widths require tighter transverse positioning and transverse rate control of the tape to maintain alignment with the transducer. For fixed position transducer applications, the tape's transverse position must be maintained to keep the reader within the boundaries of the data track. For servo mounted transducer applications, the tape's transverse position tolerance and maximum transverse rate are limited by the servo mechanism's range and frequency response.
Several patents have been issued which disclose guide mechanisms that position the tape by biasing the tape edges against multiple guide surfaces. The U.S. Pat. No. 5,610,787 issued Mar. 11, 1997 to Kunze et al., discloses a fixed tape guide structure that uses four stationary edge guides, two on each side of the transducer. In this arrangement, the inner two guides are on opposite sides of, and immediately next to the transducer. These inner guides fix the position of the tape's upper edge with respect to the transducer. The other two guides are further away from the transducer and are used to bias the tape's upper edge against the two inner guides. Tapes used with this guide mechanism must have sufficient beam strength to allow the tape to be pushed transversely by the guides without the need for additional support. The tapes must also be durable as its edges are subjected to wear sliding against four guides. Finally, the mechanism includes a positioning holder for the transducer making it suitable only for fixed position transducer applications.
The U.S. Pat. No. 5,173,828 issued Dec. 22, 1992 to Tanzer et al., discloses an apparatus that employs three flanged rolling guides on one side of a transducer, with the possibility of one or three more flanged rolling guides on the other side of the transducer. The flanges on the rolling guides provide for transverse tape positioning while the multiple guides form an arcuate path that helps stiffen the tape. This approach subjects the tape edges to wear against up to six guides, and limits the tape path and resulting space claim due to the need to guide the tape along a defined arc.
The U.S. Pat. No. 5,772,143 issued Jun. 30, 1998 to Runyon et al., discloses a tape guide mechanism in which two or three stationary guides direct the tape through a bowed path within the plane of the tape. In one embodiment, two outer guides engage the bottom edge of the tape while the middle guide presses the top edge of the tape downward causing a slight downward bow in the path of the tape. In another embodiment, the two outer guides are tilted or tapered away from each other causing a slight upward bow in the path of the tape. With this mechanism the bottom edge of the tape is subjected to wear against two guides, and the whole tape is subjected to wear as it slides against two or three stationary guides.